1. Field of the Invention
This invention relates to a solid golf ball having a good feel when hit and improved flight performance.
2. Prior Art
Solid golf balls are one-piece balls or multi-piece balls, the latter being composed either of a solid core enclosed within a cover (two-piece golf balls) or a solid core and a cover with one or more intermediate layers disposed therebetween (three or multi-piece golf balls). These solid golf balls are composed in part (the solid core, and sometimes the intermediate layer, in multi-piece golf balls) or in whole (one-piece golf balls) of an elastic portion obtained by molding and vulcanizing a rubber composition.
Conventional rubber compositions for this elastic portion are obtained by blending a base rubber composed primarily of polybutadiene rubber with a co-crosslinking agent, which is an unsaturated carboxylic acid or a metal salt thereof, in order to give the ball a certain degree of hardness and improve the impact resistance and resiliency. Through the action of a crosslinking initiator such as a peroxide, this co-crosslinking agent grafts or crosslinks to the backbone of the polybutadiene rubber, forming a three-dimensionally crosslinked polymer composed of polybutadiene and the co-crosslinking agent. This imparts a suitable degree of hardness, as well as durability and resiliency, to one-piece golf balls or to the core or intermediate layer of multi-piece golf balls, thus providing solid golf balls with a good flight performance and durability.
However, golfers have very strong desires concerning the flight performance of golf balls, today they expect even better flight performance as well as, to this end, further improvement in the resiliency of golf ball materials. In addition, the high regard for soft-type golf balls, which are solid two-piece or other multi-piece balls having softer cores to soften the feel of the ball when hit, and for spin-type balls in which soft cover stock is used to achieve improved spin performance, has also led to a heightened demand for better resiliency in golf ball materials.